The George Washington Bridge spans the Hudson River, linking New Jersey with Manhattan.

Flickr: Kevin Tsui

A leading US governor and prospective presidential candidate says he is humiliated after learning his staff organised a traffic jam on a busy bridge into New York to settle a political score.

New Jersey governor Chris Christie has also fired a top aide, saying he was lied to, and apologised to drivers who were caught up in a massive traffic snarl on the George Washington Bridge in September.

Lane closures ordered by his office, allegedly to punish the local mayor who failed to endorse Mr Christie's successful re-election bid, caused massive traffic disruption for four days in the New Jersey town of Fort Lee.

In a news conference that lasted almost two hours on Thursday, Mr Christie - one of the most powerful figures in the Republican Party and widely seen as a frontrunner for his party's 2016 presidential nomination - insisted he had been unaware of any political motive behind the lane closures until the release of emails from his aides.

"I had no knowledge or involvement in this issue, in its planning or its execution and I am stunned by the abject stupidity that was shown here," said Mr Christie, who has for months denied that any of his staff were involved.

"I am embarrassed and humiliated by the conduct of some of the people on my team.